The present invention relates generally to connector assemblies for receiving implantable leads and connecting such leads to electronic circuits within an implantable stimulation device, such as a cardiac pacemaker, and more particularly to a side actuated connector assembly having at least one lead receptacle within which an implantable lead is fixed and sealed.
Although it will become evident to those skilled in the art that the present invention is applicable to a variety of implantable tissue stimulation devices utilizing pulse generators to stimulate selected body tissue, the invention and its background will be described principally in the context of a specific example of such devices, namely, cardiac pacemakers for providing precisely controlled stimulation pulses to the heart and for receiving sensed cardiac signals via an external connector assembly having one or more lead-receiving receptacles. The appended claims are not intended to be limited, however, to any specific example or embodiment described herein.
Cardiac pacemakers, and other implantable stimulation devices such as cardiac defibrillators, are hermetically packaged to isolate the device from the body environment. Such devices require that electrical signals be reliably passed between the packaged device and its external connectors, without compromising the hermeticity of the package. Depending on the configuration of the implantable device, there may be multiple electrical paths required between the device and its external connectors for delivering, for example, multi-chamber or multi-site stimulation and shock therapy, and receiving sensed cardiac signals. These paths must be electrically and mechanically integrated with the device to provide a safe, long-term connector assembly which does not compromise the hermetic package.
Typically, a hermetic housing feedthrough electrically couples the electronic circuits contained within the device housing to a connector assembly. The feedthrough assembly extends through the hermetically sealed outer wall of the housing and into the connector assembly so as to couple the electronic circuits within the housing to lead-receiving receptacles within the connector assembly. Each lead has one or more terminals, typically in the form of a pin and one or more conductive rings. The pin is electrically coupled to a distal tip electrode and is therefore sometimes called the xe2x80x9ctip terminal.xe2x80x9d When inserted into the lead receptacle of a connector assembly, contacts within the receptacle come into contact with corresponding terminals on the lead so as to couple the lead to the electronic circuits within the implantable stimulation device via the feedthrough assembly. Needless to say, it is imperative that completely dependable electrical contact be made between the lead and the connector assembly. At the same time, the connector assembly must be capable of releasing the lead from the lead receptacle during a subsequent surgical procedure, and must also tightly seal against the entry of body fluids.
It is known in prior art connector assemblies to make electrical connection to one or more terminals on the lead by means of a variety of connector assemblies including a captive fastening screw/collet arrangement; a setscrew; and a spring or other compliant electrical contact. It is also known to use a prefabricated connector assembly to hold the electrical contacts together with a series of nonconductive spacers which are made from plastic. The resulting connector subassembly is attached to the pacemaker, or other implantable device, by fixturing it over the pacemaker and having epoxy molded around the subassembly. Alternatively, the connector subassembly may be inserted into a pre-molded connector top and bonded to the pacemaker.
In those prior art connector assemblies in which the lead is fixed within the lead receptacle using a setscrew, the setscrew is often threaded into a connector block within the connector assembly. When the screw is advanced, it comes into physical contact with the tip terminal of the lead. The resulting physical connection is often used as the electrical contact as well. However, this can present one or more problems. For example, the lead is sometimes damaged by the force produced when the setscrew is tightened. Such damage must be controlled, inasmuch as the life of the lead is often longer than that of the pacemaker. Additionally, setscrews in prior art connector assemblies have a history of stripping out of the threaded block. Particularly where relatively small setscrews are used, the threads, or the hex flats, may strip. To minimize or eliminate such problems, setscrews of a certain minimum physical size are necessary. The result is often a hump on the side of the connector assembly as the physical size of the pacemaker and its connector assembly are reduced.
A further problem of prior art setscrew type connector assemblies arises from the need to isolate the setscrew and the setscrew block from bodily fluids. One solution has been to use a silicone seal called a septum. The septum forms an insulation barrier between the setscrew and bodily fluids. However, the septum must permit a wrench to pass through it so that the screw can be tightened. Frequently, the septum is damaged by the wrench resulting in a loss of the insulation barrier.
U.S. Pat. No. 5,951,595 issued Sep. 14, 1999, and incorporated herein by reference in its entirety, discloses a connector assembly mounted on an implantable cardiac stimulation device having an actuator mechanism for fixing and tightly sealing electrical leads inserted into lead receptacles within the connector assembly without the use of setscrews. Fixing and sealing of the leads is accomplished by compressing resilient lead lock seals of O-ring shape, disposed in annular recesses, with lip portions of a plunger drawn toward a molded support by the actuator mechanism. In a first embodiment of the actuator mechanism of the ""595 patent, rotation of a cam actuator transversely journaled within the support, using a torque wrench or similar tool, moves a cam slide attached to the plunger through a fixed displacement between lock and unlock positions as an offset camming portion of the actuator engages the surfaces of a slot within the cam slide. In a second embodiment of the actuator mechanism of the ""595 patent, constant-force compression of the lead lock seals by the plunger is provided by using a torque wrench to rotate a screw actuator having one end coupled to the plunger and an opposite threaded end received within a screw block transversely disposed within the support. The screw actuator is oriented longitudinally, that is, its axis is parallel with the longitudinal axes of the lead receptacles, and includes an enlarged driver end projecting from the front end of the plunger in between the leads extending from the lead receptacles. In a third embodiment of the actuator mechanism of the ""595 patent, the actuator comprises a rotatable toothed pinion engages a toothed slot within a slidable rack to provide incremental advancement of the rack, and thereby stepped displacement and applied force, with a resulting increased resolution. In a fourth embodiment of the mechanism of the ""595 patent, compliance provided by either a spring formed within the cam slide, or a spring nut mounted thereon, prevents excessive force from being exerted on leads of larger diameter.
The connector assembly of the ""595 patent overcomes the disadvantages of earlier connector assemblies employing lead fixation techniques using setscrews. In addition, unlike the second embodiment of the ""595 patent utilizing a front actuated, longitudinally extending screw actuator, the first embodiment of the ""595 patent employing a cam actuator transversely journaled within the support has the advantage of providing unobstructed access to the actuator from the side of the assembly thereby speeding the fixation of the leads in the lead receptacles as well as their removal. A side actuated connector assembly is thus preferred by implanting physicians over a front actuated connector assembly. It has been found, however, that cam actuators do not provide the high resolution displacement of the plunger or constant force compression of the lead lock seals provided by screw actuators.
Accordingly, it would be desirable to provide a side actuated connector assembly for securing or fixing and sealing an implantable stimulation device lead within a lead receptacle that at the same time provides high resolution plunger displacement together with constant force compression of the lead lock seals.
In accordance with one specific, exemplary embodiment of the invention, there is provided a connector assembly for an implantable stimulation device, the connector assembly comprising a support having opposed sides and a longitudinally extending chamber formed therein, and a connector bore assembly coupled to and extending from the chamber in the support, the connector bore assembly being adapted to make electrical contact with a lead insertable in the chamber formed in the support. The connector assembly further includes a plunger movably coupled to the support, the plunger having a chamber aligned with the chamber in the support, the chambers in the support and in the plunger combining with the connector bore assembly to define a lead-receiving receptacle. Disposed within the lead-receiving receptacle is a locking seal, the connector assembly further comprising an actuator for selectively moving the plunger relative to the support to compress the locking seal and thereby fix a lead inserted in the lead-receiving receptacle and form a seal around said lead. The actuator includes a longitudinally extending, rotatable threaded shaft threadedly connected to the plunger and a driver element carried by the support for rotating the threaded shaft. The driver element is accessible from one of the sides of the support allowing the driver element to be rotated by means of a torque limiting wrench, for example, thus facilitating insertion and removal of the lead without obstruction.
In accordance with another aspect of the present invention, the actuator for moving the plunger is movable between a first position in which the seal engages the lead to fix the lead in place and form a seal there around and a second position in which the seal is disengaged from the lead to permit removal of the lead from the lead-receiving receptacle. Further, the threaded shaft is rotatable about a longitudinally extending axis, the driver element has an axis of rotation, and a transmission is provided for converting rotation of the driver element about the rotational axis thereof to rotation of the threaded shaft about its axis. More specifically, the longitudinal axis of the threaded shaft and the rotational axis of the driver element may be perpendicular to each other, the transmission including a bevel gear on the driver element in mesh with a driven bevel gear on the threaded shaft.
In accordance with yet another specific feature of the invention, the plunger includes a longitudinally extending, internally threaded member in threaded engagement with the threaded shaft. The threaded member on the plunger preferably comprises a split retention clamp having a plurality of longitudinally extending fingers. Further in this regard, the threaded shaft includes an outer surface and a flange projecting outwardly from the outer surface. Each of the plurality of fingers on the retention clamp includes an inwardly projecting shoulder, the shoulders on the fingers being adapted to be engaged by the flange when the actuator is fully open, thereby arresting further movement of the plunger.
It will be seen that the present invention provides a side actuated connector assembly preferred by implanting physicians, while at the same time providing by way of a screw actuator, high resolution plunger displacement together with constant force compression of the lead locking seal.
In accordance with still further embodiments of the invention, the connector assembly of the present invention can be designed to accommodate only a single lead for providing stimulation to and sensing from the tissue of a single heart chamber, or two leads for dual-chamber stimulation and single or dual-chamber sensing, or three or four leads for multi-site or multi-chamber stimulation and sensing.